This invention relates to a packet concentrating arrangement and a packet switching arrangement for use in a packet communication network in which fixed-length packets of information are propagated through communication channels.
In the manner which will later be described a little more in detail, a "knockout"switch is disclosed as a packet switching arrangement by Anthony Acampora et al in U.S. Pat. No. 4,760,570. Its operation is discussed in an article contributed by Yu-Shuan Yeh et al to IEEE Journal of Selected Areas in Communications, Volume SAC-5, No. 8 (Oct. 1987), pages 1274 to 1283, under the title of "The Knockout Switch; A Simple, Modular Architecture for High-Performance Packet Switching".
According to the Acampora et al patent, the knockout switch comprises N input terminals and N output terminals, where N represents a predetermined integer. The input terminals are for receiving N input signals, each comprising fixed-length packets in a time division sequence. A destination of the time division sequence is indicated in at least one packet. In accordance with the destination, the packets are directed through broadcast busses to a terminal group of N intermediate terminals. Such terminal groups are N in number.
A packet concentrating arrangement is connected to the terminal group and to one of the output terminals. It is therefore possible to understand that the packet concentrating arrangement comprises N "incoming"terminals and an "outgoing"terminal. A concentrator has N input ports and L output ports, where L is not greater than N. An input device is connected to the incoming terminals and to the input ports to supply packets arriving at the incoming terminals to the input ports as up to N simultaneous packets in each of successive time periods. Through a shifter, L buffers are connected to the respective output ports to buffer, as buffered packets, the simultaneous packets delivered in the concentrator from the input ports to the output ports in at least one of the time periods. A selector cyclically selects the buffers to successively supply the outgoing terminal with the buffered packets one at a time.
The knockout switch is operable with a reduced number of buffers with the buffers shared by the N incoming terminals. The knockout switch is thereby operable with a high buffer efficiency and at a high speed.
It should, however, be noted in connection with the knockout switch that the concentrator and the shifter are used as a two-stage space switch. Due to use of the space switches in two stages, the knockout switch becomes bulky and difficult to control. Usually, the output ports are less in number than the input ports. As a result, some of the simultaneous packets are discarded or lost while being processed by the concentrator. Moreover, the concentrator is complicated in structure because the concentrator comprises binary switches in a plurality of stages.